WO2020184162A1 - Thick steel sheet and production method therefor - Google Patents
Thick steel sheet and production method therefor Download PDFInfo
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- WO2020184162A1 WO2020184162A1 PCT/JP2020/007377 JP2020007377W WO2020184162A1 WO 2020184162 A1 WO2020184162 A1 WO 2020184162A1 JP 2020007377 W JP2020007377 W JP 2020007377W WO 2020184162 A1 WO2020184162 A1 WO 2020184162A1
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- Prior art keywords
- plate thickness
- less
- contained
- steel sheet
- thick steel
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 68
- 239000010959 steel Substances 0.000 title claims abstract description 68
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 15
- 239000000203 mixture Substances 0.000 claims abstract description 10
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 238000005096 rolling process Methods 0.000 claims description 26
- 238000000034 method Methods 0.000 claims description 11
- 238000010438 heat treatment Methods 0.000 claims description 7
- 229910052718 tin Inorganic materials 0.000 claims description 5
- 229910052799 carbon Inorganic materials 0.000 claims description 2
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 230000000694 effects Effects 0.000 description 20
- 229910001566 austenite Inorganic materials 0.000 description 13
- 230000007797 corrosion Effects 0.000 description 13
- 238000005260 corrosion Methods 0.000 description 13
- 238000005098 hot rolling Methods 0.000 description 13
- 238000005266 casting Methods 0.000 description 12
- 238000001816 cooling Methods 0.000 description 10
- 230000007547 defect Effects 0.000 description 10
- 238000011282 treatment Methods 0.000 description 10
- 230000007423 decrease Effects 0.000 description 9
- 239000002244 precipitate Substances 0.000 description 9
- 238000005496 tempering Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- 238000005336 cracking Methods 0.000 description 6
- 238000003860 storage Methods 0.000 description 6
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 5
- 229910052787 antimony Inorganic materials 0.000 description 5
- 230000000877 morphologic effect Effects 0.000 description 5
- 238000010791 quenching Methods 0.000 description 5
- 230000000171 quenching effect Effects 0.000 description 5
- 238000003303 reheating Methods 0.000 description 5
- 239000006104 solid solution Substances 0.000 description 5
- 238000009864 tensile test Methods 0.000 description 5
- 230000009466 transformation Effects 0.000 description 5
- 229910052758 niobium Inorganic materials 0.000 description 4
- 150000004767 nitrides Chemical class 0.000 description 4
- 229910052755 nonmetal Inorganic materials 0.000 description 4
- 230000000717 retained effect Effects 0.000 description 4
- 238000005204 segregation Methods 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 229910052721 tungsten Inorganic materials 0.000 description 4
- 229910052720 vanadium Inorganic materials 0.000 description 4
- 229910052726 zirconium Inorganic materials 0.000 description 4
- 239000010953 base metal Substances 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 239000003949 liquefied natural gas Substances 0.000 description 3
- 150000001247 metal acetylides Chemical class 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 238000004513 sizing Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000001784 detoxification Methods 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910000746 Structural steel Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- OXNIZHLAWKMVMX-UHFFFAOYSA-N picric acid Chemical compound OC1=C([N+]([O-])=O)C=C([N+]([O-])=O)C=C1[N+]([O-])=O OXNIZHLAWKMVMX-UHFFFAOYSA-N 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
- B21B3/02—Rolling special iron alloys, e.g. stainless steel
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/001—Heat treatment of ferrous alloys containing Ni
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/007—Heat treatment of ferrous alloys containing Co
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C—CHEMISTRY; METALLURGY
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/185—Hardening; Quenching with or without subsequent tempering from an intercritical temperature
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
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- C—CHEMISTRY; METALLURGY
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
Definitions
- the present invention relates to a thick steel plate suitable for structural steel used in an extremely low temperature environment such as a tank for a liquefied gas storage tank, and a method for manufacturing the same.
- the present invention relates to a thick steel sheet having excellent mechanical properties at the center of the sheet thickness, particularly excellent deformation characteristics, and a method for manufacturing the same.
- the thick steel plate in the present invention refers to a steel plate having a thickness of 6 to 80 mm.
- Thick steel sheets used in extremely low temperature environments such as tanks for liquefied gas storage tanks are required to have not only the strength of the steel sheet but also the toughness at extremely low temperatures.
- LNG liquefied natural gas
- the low temperature toughness of the steel material is inferior, the safety of the structure for the cryogenic storage tank may not be maintained. Therefore, there is a strong demand for improved low temperature toughness for the applied thick steel sheet.
- Ni-containing thick steel sheets such as 7% Ni steel sheets and 9% Ni steel sheets having a retained austenite structure that does not show brittleness at extremely low temperatures are used.
- Patent Document 1 discloses a method of refining untransformed austenite and lowering the Mf point by introducing lattice defects to stabilize a retained austenite structure that tends to become unstable at low temperature. ing. Further, in Patent Document 2, by adjusting Si, Al and N, and by controlling the Fe content in the residue after the reproduction heat cycle test, the CTD characteristics of the weld heat affected zone including the weld toe end are controlled. An excellent ultra-low temperature steel is disclosed. Further, Patent Document 3 discloses a thick steel sheet having excellent yield safety, tensile strength, and toughness value at a predetermined value or more at an extremely low temperature, and a method for manufacturing the same.
- a T-shaped joint is formed around the joint between the bottom plate and the side plate.
- the stress acting on the steel material increases, and from the viewpoint of safety, the steel material is required to have deformation performance in the plate thickness direction. Therefore, it is required to secure the deformation characteristics of the central portion of the plate thickness, which tends to be inferior in characteristics.
- the present invention has been made in view of the above problems, and an object of the present invention is to provide a thick steel sheet having excellent deformation characteristics at the center of the plate thickness and a method for manufacturing the same.
- the present invention has been made by further studying the above findings, and the gist thereof is as follows.
- C 0.01 to 0.15%
- Si 0.01 to 1.00%
- Mn 0.10 to 2.00%
- P 0.010% or less
- S It contains 0.0050% or less
- Al 0.002 to 0.100%
- Ni 5.0 to 10.0%
- N 0.0010 to 0.0080%
- a thick steel sheet having a component composition and having a drawing value of 30% or more due to tension in the plate thickness direction at the center of the plate thickness.
- a thick steel plate having excellent deformation characteristics at the center of the plate thickness can be obtained.
- the thick steel plate of the present invention greatly contributes to improving the safety of steel structures used in extremely low temperature environments such as tanks for liquefied gas storage tanks, and brings about a remarkable industrial effect.
- % representing a component composition shall mean mass% unless otherwise specified.
- C 0.01-0.15%
- C is effective for increasing the strength, and in order to obtain the effect, C needs to be contained in an amount of 0.01% or more. It is preferably 0.03% or more.
- C is set to 0.15% or less. It is preferably 0.10% or less.
- Si 0.01-1.00% Si is not only necessary in the steelmaking process because it acts as a deoxidizing agent, but also has the effect of increasing the strength of the steel sheet by solid solution strengthening by solid solution in steel. In order to obtain such an effect, Si needs to have a content of 0.01% or more. On the other hand, if it is contained in excess of 1.00%, the weldability and surface properties are deteriorated. Therefore, Si is set to 1.00% or less. It is preferably 0.5% or less. More preferably, it is 0.3% or less.
- Mn 0.10 to 2.00%
- Mn is an element that enhances the hardenability of steel sheets and is effective in increasing the strength. In order to obtain this effect, Mn needs to be contained in an amount of 0.10% or more. Preferably, it is 0.40% or more. On the other hand, when the content exceeds 2.00%, the center segregation is promoted, which causes a decrease in cryogenic toughness, deterioration of the drawing value due to tension in the plate thickness direction at the center of the plate thickness, and occurrence of stress corrosion cracking.
- Mn is set to 2.00% or less. Preferably, it is 1.00% or less.
- P 0.010% or less.
- S 0.0050% or less S forms MnS in steel and significantly deteriorates low temperature toughness and drawing value due to tension in the plate thickness direction at the center of plate thickness. Therefore, it is desirable to reduce S as much as possible, and S is 0.0050% or less. It is preferably 0.0020% or less.
- Al acts as a deoxidizer and is most commonly used in the molten steel deoxidation process. Further, it has the effect of fixing the solid solution N in the steel to form AlN and suppressing the deterioration of toughness due to the reduction of the solid solution N. In order to obtain this effect, Al needs to be contained in an amount of 0.002% or more. It is preferably 0.010% or more. More preferably, it is 0.020% or more. On the other hand, if the content exceeds 0.100%, it diffuses into the weld metal portion during welding and the toughness of the weld metal deteriorates, so the content is set to 0.100% or less. It is preferably 0.070% or less. More preferably, it is 0.060% or less.
- Ni 5.0-10.0%
- Ni is an element that is extremely effective in improving the low temperature toughness of steel sheets by increasing the strength of the steel sheets and stabilizing retained austenite. Since Ni is an expensive element, the cost of steel sheet increases as its content increases. Therefore, the Ni content is set to 10.0% or less. On the other hand, when the Ni content is less than 5.0%, the strength of the steel sheet is lowered, and stable retained austenite cannot be obtained at a low temperature, and as a result, the low temperature toughness and strength of the steel sheet are lowered. Therefore, Ni is set to 5.0% or more. Preferably, it is 6.0 to 9.0%.
- N is an austenite stabilizing element and is an element effective for improving cryogenic toughness. Further, it has an effect of suppressing stress corrosion cracking as a trap site of diffusible hydrogen by binding to Nb, V and Ti and finely precipitating as a nitride or carbonitride. In order to obtain such an effect, N needs to be contained in an amount of 0.0010% or more. It is preferably 0.0020% or more. On the other hand, if it is contained in excess of 0.0080%, not only the formation of excess nitride or carbonitride is promoted, the amount of solid solution elements is lowered and the corrosion resistance is lowered, but also the toughness and the plate thickness direction at the center of the plate thickness are reduced. The drawing value due to tension decreases. Therefore, N is set to 0.0.0080% or less. It is preferably 0.0060% or less.
- Cr 0.01 to 1.50%
- Mo 0.03 to 1.0
- % 0.001 to 0.030%
- V 0.01 to 0.10%
- Ti 0.003 to 0.050%
- B 0.0003 to 0.0100%
- Cu 0. It can contain one or more selected from 01 to 1.00%.
- Cr 0.01 to 1.50% Cr is an element effective for increasing the strength. In order to obtain the effect, when Cr is contained, is set to 0.01% or more. On the other hand, Cr may be precipitated in the form of nitrides, carbides, carbonitrides, etc. during rolling, and the formation of such precipitates becomes a starting point of corrosion and fracture, and the low temperature toughness is lowered. Therefore, when it is contained, the amount of Cr is set to 1.50% or less. More preferably, the amount of Cr is 1.00% or less.
- Mo 0.03 to 1.0%
- Mo is an element effective in suppressing the temper embrittlement susceptibility of a steel sheet, and is also an element capable of obtaining steel sheet strength without impairing low temperature toughness.
- the content is 0.03% or more. More preferably, it is more than 0.05%.
- the low temperature toughness decreases. Therefore, when Mo is contained, the content is preferably 1.0% or less. More preferably, it is 0.30% or less.
- Nb is an element effective for improving the strength of the steel sheet.
- the content is 0.001% or more. It is more preferably 0.005% or more, still more preferably 0.007% or more.
- coarse carbonitride may be precipitated, which may become a starting point of fracture and deteriorate the tensile property in the plate thickness direction at the center of the plate thickness.
- the precipitate may become coarse and the toughness of the base metal may be deteriorated. Therefore, when Nb is contained, it is set to 0.030% or less. It is more preferably 0.025% or less, still more preferably 0.022% or less.
- V 0.01 to 0.10%
- V is an element effective for improving the strength of the steel sheet.
- the content is 0.01% or more. It is more preferably 0.02% or more, still more preferably 0.03% or more.
- coarse carbonitride may be precipitated and become a starting point of fracture.
- the precipitate may become coarse and the toughness of the base metal may be deteriorated. Therefore, when V is contained, it is set to 0.10% or less. It is more preferably 0.09% or less, still more preferably 0.08% or less.
- Ti 0.003 to 0.050%
- Ti is an element that precipitates as a nitride or carbonitride and is effective in improving the strength of a steel sheet.
- the content is 0.003% or more. It is more preferably 0.005% or more, still more preferably 0.007% or more.
- the precipitate may become coarse and the toughness of the base metal may be deteriorated.
- coarse carbonitride may precipitate and serve as a starting point for fracture. Therefore, when Ti is contained, it is set to 0.050% or less. It is more preferably 0.035% or less, still more preferably 0.032% or less.
- B 0.0003 to 0.0100%
- B is an element effective for improving the strength of the base material. In order to obtain such an effect, when B is contained, the content is 0.0003% or more. On the other hand, if it is contained in excess of 0.0100%, a coarse B precipitate is formed and the toughness is lowered. Therefore, when B is contained, it is set to 0.0100% or less. More preferably, it is 0.0030% or less.
- Cu 0.01-1.00%
- Cu is an effective element that enhances the strength of steel sheets by improving hardenability.
- the content is 0.01% or more.
- the content exceeds 1.00%, the low temperature toughness of the steel sheet is lowered, and the properties of the steel (slab) surface after casting may be deteriorated. Therefore, when Cu is contained, it is set to 1.00% or less. More preferably, it is 0.30% or less.
- Sn 0.01 to 0.30%
- Sb 0.01 to 0.30%
- W more than 0 to 2.00%
- Co more than 0 to 2.
- Sn 0.01 to 0.30%
- Sn is an element effective for improving corrosion resistance. These elements are effective even if they are contained in a small amount, but when Sn is contained, the content is 0.01% or more. However, if it is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, when Sn is contained, it is set to 0.30% or less. More preferably, it is 0.25% or less.
- Sb 0.01 to 0.30% Similar to Sn, Sb is an element effective for improving corrosion resistance. These elements are effective even if they are contained in a small amount, but when Sb is contained, the content is 0.01% or more. However, if it is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, when Sb is contained, it is set to 0.30% or less. More preferably, it is 0.25% or less.
- W Over 0 to 2.00% Like Sn and Sb, W is an element effective for improving corrosion resistance. Since these elements are effective even when contained in a small amount, W can be contained in excess of 0%. However, if it is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, when W is contained, it is set to 2.00% or less. More preferably, it is 0.50% or less.
- Co is an element effective for improving corrosion resistance, like Sn, Sb, and W. Since these elements are effective even when contained in a small amount, Co can be contained in excess of 0%. More preferably, it is 0.10% or more. However, if it is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, when Co is contained, it is set to 2.00% or less. More preferably, it is 1.50% or less.
- Ca 0.0005 to 0.0050%
- Ca is an element effective for controlling the morphology of inclusions such as MnS, and can be contained as needed.
- Morphological control of inclusions means that the expanded sulfide-based inclusions are made into granular inclusions. Through the morphological control of the inclusions, the tensile properties in the plate thickness direction, the toughness, and the sulfide stress corrosion cracking resistance of the central portion of the plate thickness can be improved.
- the content is 0.0005% or more. More preferably, it is 0.0010% or more.
- Ca when a large amount of Ca is contained, the amount of non-metal inclusions increases, and the tensile characteristics in the plate thickness direction at the center of the plate thickness may decrease. Therefore, when Ca is contained, it is set to 0.0050% or less. More preferably, it is 0.0040% or less.
- Mg is an element effective for controlling the morphology of inclusions such as MnS, and can be contained as needed. Through the morphological control of the inclusions, the tensile properties in the plate thickness direction, the toughness, and the sulfide stress corrosion cracking resistance of the central portion of the plate thickness can be improved. In order to obtain such an effect, when Mg is contained, the content is 0.0005% or more. More preferably, it is 0.0010% or more. On the other hand, when a large amount of Mg is contained, the amount of non-metal inclusions increases, and the tensile characteristics in the plate thickness direction at the center of the plate thickness may decrease. Therefore, when Mg is contained, it is set to 0.0050% or less. More preferably, it is 0.0040% or less.
- Zr 0.0005-0.0050%
- Zr is an element effective for controlling the morphology of inclusions such as MnS, and can be contained as needed. Through the morphological control of the inclusions, the tensile properties in the plate thickness direction, the toughness, and the sulfide stress corrosion cracking resistance at the center of the plate thickness can be improved. In order to obtain such an effect, Zr is set to 0.0005% or more. It is preferably 0.0010% or more. On the other hand, when a large amount of Zr is contained, the amount of non-metal inclusions increases, and the tensile characteristics in the plate thickness direction at the center of the plate thickness may decrease. Therefore, when Zr is contained, it is set to 0.0050% or less. More preferably, it is 0.0040% or less.
- REM 0.0010-0.0100%
- the REM is an element effective for controlling the morphology of inclusions such as MnS, and can be contained as needed. Through the morphological control of the inclusions, the tensile properties in the plate thickness direction, the toughness, and the sulfide stress corrosion cracking resistance at the center of the plate thickness can be improved. In order to obtain such an effect, the REM is set to 0.0010% or more. More preferably, it is 0.0020% or more. On the other hand, if a large amount of REM is contained, the amount of non-metal inclusions may increase, and the tensile characteristics in the plate thickness direction at the center of the plate thickness may decrease. Therefore, when REM is contained, it should be 0.0100% or less.
- the balance is Fe and unavoidable impurities.
- the thick steel plate in the present invention has a deformation characteristic in which the drawing value due to tension in the plate thickness direction at the center of the plate thickness is 30% or more.
- the drawing value is a fraction ( ⁇ S / S (%)) of the amount of decrease in the cross-sectional area of the test piece after the test, ⁇ S, with respect to the cross-sectional area S of the test piece before the test in the tensile test.
- the aperture value is preferably 35% or more.
- the drawing value of the present invention can be obtained by controlling the light rolling conditions at the time of casting and / or the conditions at the time of finish rolling, which will be described later.
- MnS having a major axis of 100 ⁇ m or more is 10 pieces / mm 2 or less and the old austenite grains have a circular equivalent diameter of less than 100 ⁇ m in the central portion of the plate thickness. This is because stress concentration occurs in casting defects, coarse MnS, and coarse old austenite grains, and is likely to be a starting point of fracture.
- the desired MnS can be obtained by controlling the light reduction during continuous casting, which will be described later.
- the central portion of the plate thickness in the present invention indicates a plate thickness 1/2 position
- the aperture value, MnS and the former austenite grains are the values measured by the measuring method described in Examples described later.
- the temperature "° C.” means the temperature at the center of the plate thickness.
- a slab having a desired composition is heated to 1000 ° C. or higher and 1300 ° C. or lower, and then during finish rolling, a reduction ratio of 3 or more and at least 2 of the final 3 passes are performed. Hot rolling is performed so that the rolling shape ratio per pass is 0.7 or more.
- Reheating temperature of steel material 1000 ° C or higher and 1300 ° C or lower
- the reason for reheating the steel material is to dissolve the precipitates in the structure and make the crystal grain size uniform, and the heating temperature is 1000.
- the temperature is equal to or higher than 1300 ° C.
- the heating temperature is less than 1000 ° C., not only the precipitates such as AlN do not dissolve sufficiently, but also they become coarse during reheating and become the starting point of fracture, so that the drawing value in the desired tensile test in the plate thickness direction can be obtained. Absent.
- the reheating temperature is set to 1300 ° C. or lower.
- the temperature is preferably 1250 ° C or lower, more preferably 1200 ° C or lower.
- the reheating time is preferably 1 to 10 hours.
- the reduction ratio of the finish rolling is 3 or more.
- the reduction ratio (slab thickness / final plate thickness) is set to 3 or more to promote recrystallization and sizing, and to achieve porosity. Casting defects such as so-called internal micropores can be crimped to make them harmless. Further, by reducing the central segregation of Mn, P, S and the like, it is possible to obtain a desired tensile property in the plate thickness direction as a desired hot-rolled plate microstructure. In hot rolling with a reduction ratio of less than 3, a desired microstructure cannot be obtained due to residual coarse structure, insufficient detoxification of the casting defects and central segregation, etc., and in a tensile test in a desired plate thickness direction. I can't get the aperture value. Therefore, the reduction ratio is limited to 3 or more.
- the reduction ratio is preferably 4 or more, and more preferably 5 or more.
- Rolled shape ratio per pass for at least 2 of the final 3 passes that finally determine the material By setting the value to 0.7 or more, casting defects can be reliably detoxified, and coarse grains can be suppressed from remaining in the entire steel sheet, particularly in the central portion of the sheet thickness, for sizing. As a result, the drawing value due to tension in the plate thickness direction at the center of the plate thickness is improved.
- the rolling shape ratio (ld / h m ) is ⁇ the length of the rolled roll in contact with the steel plate (roll contact arc length: ld) ⁇ / ⁇ the average of the plate thickness on the roll entry side and the plate thickness on the exit side.
- h m ⁇ refers to h m ⁇ , represented by formula (1).
- ld / h m ⁇ R ( h i -h o) ⁇ 1/2 / ⁇ (h i + 2h o) / 3 ⁇ here, R: Roll radius at each rolling pass h i : Incoming plate thickness at each rolling pass h 0 : Outer plate thickness at each rolling pass. If the number of passes having a rolled shape ratio of 0.7 or more is less than 2 passes, a desired microstructure cannot be obtained, such as a coarse structure remaining or insufficient detoxification of casting defects, and a desired plate thickness center portion. The drawing value due to tension in the plate thickness direction cannot be obtained. Therefore, at least two passes have a rolled shape ratio of 0.7 or more. In order to increase the rolling shape ratio, the rolling roll diameter may be increased or the rolling reduction amount may be increased.
- the manufacturing conditions other than the above are not particularly limited, but it is preferable to carry out under the following conditions.
- the slab during continuous casting it is preferable to lightly reduce the slab during continuous casting.
- by lightly reducing the pressure it is possible to further suppress the residual of coarse MnS having a major axis of 100 ⁇ m or more and coarse old austenite grains having a circular equivalent diameter of 100 ⁇ m or more in the central portion of the plate thickness.
- the reduction gradient is 0.1 mm / m or more upstream of the final solidification position of the slab.
- Cooling start temperature after hot rolling is not particularly limited, and is preferably 1000 ° C. or lower and 500 ° C. or higher.
- the cooling method after hot hot rolling is not particularly limited, and any method such as air cooling or water cooling can be used.
- water cooling such as spray cooling, mist cooling, and laminar cooling may be performed after hot rolling.
- the final product can be cooled after hot rolling, but it is preferable to perform heat treatment in order to further obtain necessary properties such as low temperature toughness.
- a tempering treatment after hot rolling it is preferable to perform a tempering treatment after hot rolling.
- a quenching-tempering treatment may be performed in which a quenching treatment is also performed before the tempering treatment.
- a two-phase region quenching-tempering treatment in which a tempering treatment is performed after the two-phase region quenching treatment may be performed.
- the quenching-two-phase quenching-tempering treatment may be performed with the two-phase region quenching treatment sandwiched between the quenching-tempering treatments. It is desirable to manufacture using any of the above processes.
- the quenching temperature is preferably Ac 3 transformation point or more and 1000 ° C. or less.
- the quenching temperature in the two-phase region is preferably at least the Ac 1 transformation point and below the Ac 3 transformation point.
- the tempering temperature is preferably 500 to 650 ° C.
- the Ac 3 transformation point and the Ac 1 transformation point can be obtained by the following equations (1) and (2).
- Ac 1 (° C.) 750.8-26.6C + 17.6Si-11.6Mn-22.9Cu-23Ni + 24.1Cr + 22.5Mo-39.7V-5.7Ti + 232.4Nb-169.4Al ...
- Ac 3 (° C.) 937.2-436.5C + 56Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr + 38.1Mo + 124.8V + 136.3Ti-19.1Nb + 198.4Al ...
- the element symbol in the above formulas (1) and (2) represents the content (mass%) of each element, and is set to 0 when the element is not contained.
- the obtained thick steel sheet was subjected to the following test.
- the thickness direction of the thick steel plate was set to be the tensile direction, and the test piece was processed into a Type A-shaped test piece, and a tensile test was carried out in accordance with JIS G3199.
- the test piece was collected so that the thickness direction of the thick steel plate was the tensile direction, and the test piece was cooled to -196 ° C in liquid nitrogen and subjected to a Charpy impact test in accordance with JIS Z2242. to determine the absorption energy vE -196 at 196 °C.
- the yield strength (YS) is 585 MPa or more
- the tensile strength (TS) is 690 MPa or more
- the drawing value after fracture the amount of decrease in the cross-sectional area of the test piece after the test with respect to the cross-sectional area S of the test piece before the test in the tensile test ⁇ S). fraction
- test pieces for microstructure observation were collected so that the plate thickness 1/2 position was the observation position.
- the test piece was embedded in resin so that the cross section perpendicular to the rolling direction was the observation surface, and mirror-polished.
- observation was performed with an SEM at a magnification of 200 times, and an SEM image of the structure at a plate thickness of 1/2 was taken.
- the images of the five visual fields taken were analyzed by an image analysis device, and the number density of MnS having a major axis of 100 ⁇ m or more and the maximum value of the equivalent circle diameter of the old austenite grains were obtained.
- Table 2 shows the results obtained from the above.
- Examples of the present invention (Samples Nos. 1 to 15, 27 to 29, 31 to 32) satisfy a drawing value of 30% or more, and are excellent in both strength and low temperature toughness.
- the comparative examples (Sample Nos. 16 to 26, 30) outside the scope of the present invention are inferior in at least one of the drawing value, strength, and low temperature toughness.
Abstract
Description
1.板厚中心部における板厚方向引張による絞り値を制御することにより、板厚中心部の変形性能を向上させることができる。
2.熱間圧延工程の仕上圧延において、圧下比3以上かつ最終3パスのうち少なくとも2パスについて、1パス当たりの圧延形状比が0.7以上の圧延を行うことで、鋳造欠陥、板厚中心部での粗大粒を抑制し鋼板全体を整粒化することができ、板厚中心部における板厚方向引張特性(絞り値)を改善することができる。
3.板厚中心部における板厚方向引張特性(絞り値)において、板厚中心部に存在する鋳造欠陥および長径100μm以上の粗大なMnSが多いほど、より絞り値が低い。また、円相当径で100μm以上の粗大な旧オーステナイト粒が存在するほど、より絞り値が低い。これは、鋳造欠陥、粗大なMnSおよび粗大な旧オーステナイト粒で応力集中が生じ、破壊の起点となるためである。
4.Sの含有量を0.0050%以下に制御し、さらに連続鋳造時の軽圧下による中心偏析低減により、鋳造欠陥、粗大なMnSを低減させ、板厚中心部における板厚方向引張特性(絞り値)をより改善することができる。 In order to achieve the above problems, the present inventors have conducted intensive research on the composition of steel sheets and the manufacturing method for thick steel sheets containing Ni, which are suitable for structural steels used in an extremely low temperature environment. The following findings were obtained.
1. 1. By controlling the drawing value due to the tension in the plate thickness direction at the plate thickness center portion, the deformation performance of the plate thickness center portion can be improved.
2. 2. In the finish rolling of the hot rolling process, rolling with a rolling shape ratio of 0.7 or more per pass for at least 2 of the final 3 passes with a rolling reduction ratio of 3 or more causes casting defects and the center of the plate thickness. It is possible to suppress the coarse grain in the sheet and to sizing the entire steel sheet, and to improve the tensile property (rolling value) in the plate thickness direction at the center of the plate thickness.
3. 3. In the tensile characteristics (drawing value) in the plate thickness direction at the center of the plate thickness, the more casting defects existing in the center of the plate thickness and the coarse MnS having a major axis of 100 μm or more, the lower the drawing value. Further, the more coarse old austenite grains having a diameter equivalent to a circle of 100 μm or more are present, the lower the drawing value is. This is because stress concentration occurs in casting defects, coarse MnS and coarse old austenite grains, which is a starting point of fracture.
4. By controlling the S content to 0.0050% or less and reducing central segregation under light pressure during continuous casting, casting defects and coarse MnS are reduced, and tensile characteristics in the plate thickness direction (drawing value) at the center of the plate thickness. ) Can be further improved.
[1]質量%で、C:0.01~0.15%、Si:0.01~1.00%、Mn:0.10~2.00%、P:0.010%以下、S:0.0050%以下、Al:0.002~0.100%、Ni:5.0~10.0%、N:0.0010~0.0080%を含有し、残部Feおよび不可避的不純物からなる成分組成を有し、板厚中心部における板厚方向引張による絞り値が30%以上である厚鋼板。
[2]さらに質量%で、Cr:0.01~1.50%、Mo:0.03~1.0%、Nb:0.001~0.030%、V:0.01~0.10%、Ti:0.003~0.050%、B:0.0003~0.0100%、Cu:0.01~1.00%から選択される1種または2種以上を含有する[1]に記載の厚鋼板。
[3]さらに質量%で、Sn:0.01~0.30%、Sb:0.01~0.30%、W:0超~2.00%、Co:0超~2.00%、Ca:0.0005~0.0050%、Mg:0.0005~0.0050%、Zr:0.0005~0.0050%、REM:0.0010~0.0100%から選択される1種または2種以上を含有する[1]または[2]に記載の厚鋼板。
[4][1]~[3]のいずれかに記載の成分組成からなるスラブを、1000℃以上1300℃以下に加熱したのち、仕上圧延の際、圧下比3以上かつ最終3パスのうち少なくとも2パスについて、1パス当たりの圧延形状比が0.7以上とする熱間圧延を行う厚鋼板の製造方法。 The present invention has been made by further studying the above findings, and the gist thereof is as follows.
[1] In terms of mass%, C: 0.01 to 0.15%, Si: 0.01 to 1.00%, Mn: 0.10 to 2.00%, P: 0.010% or less, S: It contains 0.0050% or less, Al: 0.002 to 0.100%, Ni: 5.0 to 10.0%, N: 0.0010 to 0.0080%, and consists of the balance Fe and unavoidable impurities. A thick steel sheet having a component composition and having a drawing value of 30% or more due to tension in the plate thickness direction at the center of the plate thickness.
[2] Further, in mass%, Cr: 0.01 to 1.50%, Mo: 0.03 to 1.0%, Nb: 0.001 to 0.030%, V: 0.01 to 0.10. %, Ti: 0.003 to 0.050%, B: 0.0003 to 0.0100%, Cu: 0.01 to 1.00%, and contains one or more selected from [1]. The thick steel plate described in.
[3] Further, in terms of mass%, Sn: 0.01 to 0.30%, Sb: 0.01 to 0.30%, W: more than 0 to 2.00%, Co: more than 0 to 2.00%, One selected from Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0050%, Zr: 0.0005 to 0.0050%, REM: 0.0010 to 0.0100% or The thick steel plate according to [1] or [2], which contains two or more kinds.
[4] A slab having the component composition according to any one of [1] to [3] is heated to 1000 ° C. or higher and 1300 ° C. or lower, and then rolled at a reduction ratio of 3 or more and at least one of the final 3 passes. A method for manufacturing a thick steel sheet by hot rolling in which the rolling shape ratio per pass is 0.7 or more for 2 passes.
Cは、高強度化に有効で、その効果を得るためには、Cは0.01%以上の含有を必要とする。好ましくは0.03%以上とする。一方、0.15%を超えて含有すると、板厚中心部に偏析し、Cr炭化物およびNb、V、Ti系炭化物の過度な析出を促すため、低温靱性が低下するとともに、絞り値が低下する。このため、Cは0.15%以下とする。好ましくは0.10%以下とする。 C: 0.01-0.15%
C is effective for increasing the strength, and in order to obtain the effect, C needs to be contained in an amount of 0.01% or more. It is preferably 0.03% or more. On the other hand, if it is contained in excess of 0.15%, it segregates in the center of the plate thickness and promotes excessive precipitation of Cr carbides and Nb, V, Ti-based carbides, so that the low temperature toughness is lowered and the drawing value is lowered. .. Therefore, C is set to 0.15% or less. It is preferably 0.10% or less.
Siは、脱酸剤として作用するため製鋼プロセスにおいて必要であるだけでなく、鋼に固溶して固溶強化により鋼板を高強度化する効果を有する。このような効果を得るために、Siは0.01%以上の含有を必要とする。一方、1.00%を超えて含有すると、溶接性および表面性状が劣化する。このため、Siは1.00%以下とする。好ましくは0.5%以下とする。より好ましくは0.3%以下とする。 Si: 0.01-1.00%
Si is not only necessary in the steelmaking process because it acts as a deoxidizing agent, but also has the effect of increasing the strength of the steel sheet by solid solution strengthening by solid solution in steel. In order to obtain such an effect, Si needs to have a content of 0.01% or more. On the other hand, if it is contained in excess of 1.00%, the weldability and surface properties are deteriorated. Therefore, Si is set to 1.00% or less. It is preferably 0.5% or less. More preferably, it is 0.3% or less.
Mnは、鋼板の焼き入れ性を高め、高強度化に有効な元素である。この効果を得るために、Mnは0.10%以上の含有を必要とする。好ましくは、0.40%以上とする。一方、2.00%を超えて含有する場合、中心偏析を助長し、極低温靭性の低下や板厚中心部における板厚方向引張による絞り値の劣化、応力腐食割れの発生を引き起こす。また、板厚中心部において、破壊の起点となる長径が100μm以上の粗大なMnSの生成を助長し、板厚方向引張による絞り値を著しく劣化させる。このため、Mnは2.00%以下とする。好ましくは、1.00%以下とする。 Mn: 0.10 to 2.00%
Mn is an element that enhances the hardenability of steel sheets and is effective in increasing the strength. In order to obtain this effect, Mn needs to be contained in an amount of 0.10% or more. Preferably, it is 0.40% or more. On the other hand, when the content exceeds 2.00%, the center segregation is promoted, which causes a decrease in cryogenic toughness, deterioration of the drawing value due to tension in the plate thickness direction at the center of the plate thickness, and occurrence of stress corrosion cracking. Further, in the central portion of the plate thickness, the generation of coarse MnS having a major axis of 100 μm or more, which is the starting point of fracture, is promoted, and the drawing value due to tension in the plate thickness direction is significantly deteriorated. Therefore, Mn is set to 2.00% or less. Preferably, it is 1.00% or less.
Pは、0.010%を超えて含有すると、粒界に偏析し粒界強度を低下させ、破壊起点となり、その結果、板厚中心部における板厚方向引張による絞り値が低下する。そのため、Pは可能なかぎり低減することが望ましく、Pは0.010%以下とする。 P: 0.010% or less When P is contained in excess of 0.010%, it segregates at the grain boundaries and lowers the grain boundary strength, which becomes a fracture starting point. As a result, drawing by tension in the plate thickness direction at the center of the plate thickness. The value drops. Therefore, it is desirable to reduce P as much as possible, and P is 0.010% or less.
Sは鋼中でMnSを形成し低温靭性や板厚中心部における板厚方向引張による絞り値を著しく劣化させる。そのため、Sは可能なかぎり低減することが望ましく、Sは0.0050%以下とする。好ましくは0.0020%以下とする。 S: 0.0050% or less S forms MnS in steel and significantly deteriorates low temperature toughness and drawing value due to tension in the plate thickness direction at the center of plate thickness. Therefore, it is desirable to reduce S as much as possible, and S is 0.0050% or less. It is preferably 0.0020% or less.
Alは脱酸剤として作用し溶鋼脱酸プロセスにおいて、最も汎用的に使用される。また、鋼中の固溶Nを固定してAlNを形成し、固溶N低減による靱性劣化を抑制する効果を有する。この効果を得るために、Alは0.002%以上の含有を必要とする。好ましくは0.010%以上とする。より好ましくは0.020%以上とする。一方、0.100%を超えて含有すると、溶接時に溶接金属部に拡散して、溶接金属の靭性が劣化するため、0.100%以下とする。好ましくは0.070%以下とする。より好ましくは0.060%以下とする。 Al: 0.002 to 0.100%
Al acts as a deoxidizer and is most commonly used in the molten steel deoxidation process. Further, it has the effect of fixing the solid solution N in the steel to form AlN and suppressing the deterioration of toughness due to the reduction of the solid solution N. In order to obtain this effect, Al needs to be contained in an amount of 0.002% or more. It is preferably 0.010% or more. More preferably, it is 0.020% or more. On the other hand, if the content exceeds 0.100%, it diffuses into the weld metal portion during welding and the toughness of the weld metal deteriorates, so the content is set to 0.100% or less. It is preferably 0.070% or less. More preferably, it is 0.060% or less.
Niは、鋼板の強度を上昇させるとともに残留オーステナイトを安定化し、鋼板の低温靭性の向上に極めて有効な元素である。Niは高価な元素であるため、その含有量が高くなるにつれて鋼板コストが高騰する。このため、Ni含有量を10.0%以下とする。一方、Ni含有量が5.0%未満になると、鋼板強度が低下するほか、低温で安定した残留オーステナイトが得られなくなり、その結果、鋼板の低温靭性や強度が低下する。したがって、Niは5.0%以上とする。好ましくは、6.0~9.0%である。 Ni: 5.0-10.0%
Ni is an element that is extremely effective in improving the low temperature toughness of steel sheets by increasing the strength of the steel sheets and stabilizing retained austenite. Since Ni is an expensive element, the cost of steel sheet increases as its content increases. Therefore, the Ni content is set to 10.0% or less. On the other hand, when the Ni content is less than 5.0%, the strength of the steel sheet is lowered, and stable retained austenite cannot be obtained at a low temperature, and as a result, the low temperature toughness and strength of the steel sheet are lowered. Therefore, Ni is set to 5.0% or more. Preferably, it is 6.0 to 9.0%.
Nは、オーステナイト安定化元素であり、極低温靱性の向上に有効な元素である。また、Nb、V、Tiと結合し、窒化物または炭窒化物として微細に析出して、拡散性水素のトラップサイトとして応力腐食割れを抑制する効果を有する。このような効果を得るためには、Nは0.0010%以上の含有を必要とする。好ましくは0.0020%以上とする。一方、0.0080%を超えて含有すると、過剰な窒化物または炭窒化物の生成を促し、固溶元素量が低下し耐食性が低下するだけでなく、靭性および板厚中心部における板厚方向引張による絞り値が低下する。このため、Nは0.0.0080%以下とする。好ましくは0.0060%以下とする。 N: 0.0010 to 0.0080%
N is an austenite stabilizing element and is an element effective for improving cryogenic toughness. Further, it has an effect of suppressing stress corrosion cracking as a trap site of diffusible hydrogen by binding to Nb, V and Ti and finely precipitating as a nitride or carbonitride. In order to obtain such an effect, N needs to be contained in an amount of 0.0010% or more. It is preferably 0.0020% or more. On the other hand, if it is contained in excess of 0.0080%, not only the formation of excess nitride or carbonitride is promoted, the amount of solid solution elements is lowered and the corrosion resistance is lowered, but also the toughness and the plate thickness direction at the center of the plate thickness are reduced. The drawing value due to tension decreases. Therefore, N is set to 0.0.0080% or less. It is preferably 0.0060% or less.
Crは、強度を上昇させるのに有効な元素である。その効果を得るためには、Crを含有する場合は、は0.01%以上とする。一方で、Crは圧延中に窒化物、炭化物、炭窒化物等の形態で析出する場合があり、このような析出物の形成により腐食や破壊の起点となって低温靭性が低下する。このため、含有する場合、Cr量は1.50%以下にする。より好ましくはCr量が1.00%以下とする。 Cr: 0.01 to 1.50%
Cr is an element effective for increasing the strength. In order to obtain the effect, when Cr is contained, is set to 0.01% or more. On the other hand, Cr may be precipitated in the form of nitrides, carbides, carbonitrides, etc. during rolling, and the formation of such precipitates becomes a starting point of corrosion and fracture, and the low temperature toughness is lowered. Therefore, when it is contained, the amount of Cr is set to 1.50% or less. More preferably, the amount of Cr is 1.00% or less.
Moは、鋼板の焼戻し脆化感受性を抑制するのに有効な元素であり、また、低温靭性を損なうことなく鋼板強度が得られる元素でもある。このような効果を得るためには、Moを含有する場合は、0.03%以上とする。より好ましくは0.05%超とする。一方、1.0%を超えると低温靭性が低下する。したがって、Moを含有させる場合には、その含有量1.0%以下とすることが好ましい。より好ましくは0.30%以下である。 Mo: 0.03 to 1.0%
Mo is an element effective in suppressing the temper embrittlement susceptibility of a steel sheet, and is also an element capable of obtaining steel sheet strength without impairing low temperature toughness. In order to obtain such an effect, when Mo is contained, the content is 0.03% or more. More preferably, it is more than 0.05%. On the other hand, if it exceeds 1.0%, the low temperature toughness decreases. Therefore, when Mo is contained, the content is preferably 1.0% or less. More preferably, it is 0.30% or less.
Nbは、鋼板の強度の向上に有効な元素である。このような効果を得るためには、Nbを含有する場合は、0.001%以上とする。より好ましくは0.005%以上、さらに好ましくは0.007%以上とする。一方、0.030%を超えて含有すると、粗大な炭窒化物が析出し、破壊の起点となり、板厚中心部における板厚方向引張特性を劣化させることがある。また、析出物が粗大化し、母材靱性を劣化させることがある。このため、Nbを含有する場合は、0.030%以下とする。より好ましくは0.025%以下、さらに好ましくは0.022%以下である。 Nb: 0.001 to 0.030%
Nb is an element effective for improving the strength of the steel sheet. In order to obtain such an effect, when Nb is contained, the content is 0.001% or more. It is more preferably 0.005% or more, still more preferably 0.007% or more. On the other hand, if it is contained in excess of 0.030%, coarse carbonitride may be precipitated, which may become a starting point of fracture and deteriorate the tensile property in the plate thickness direction at the center of the plate thickness. In addition, the precipitate may become coarse and the toughness of the base metal may be deteriorated. Therefore, when Nb is contained, it is set to 0.030% or less. It is more preferably 0.025% or less, still more preferably 0.022% or less.
Vは、鋼板の強度向上に有効な元素である。このような効果を得るためには、Vを含有する場合は、0.01%以上とする。より好ましくは0.02%以上、さらに好ましくは0.03%以上とする。一方、0.10%を超えて含有すると、粗大な炭窒化物が析出し、破壊の起点となることがある。また、析出物が粗大化し、母材靱性を劣化させることがある。このため、Vを含有する場合は、0.10%以下とする。より好ましくは0.09%以下、さらに好ましくは0.08%以下とする。 V: 0.01 to 0.10%
V is an element effective for improving the strength of the steel sheet. In order to obtain such an effect, when V is contained, the content is 0.01% or more. It is more preferably 0.02% or more, still more preferably 0.03% or more. On the other hand, if it is contained in an amount of more than 0.10%, coarse carbonitride may be precipitated and become a starting point of fracture. In addition, the precipitate may become coarse and the toughness of the base metal may be deteriorated. Therefore, when V is contained, it is set to 0.10% or less. It is more preferably 0.09% or less, still more preferably 0.08% or less.
Tiは、窒化物もしくは炭窒化物として析出し、鋼板の強度向上に有効な元素である。このような効果を得るためには、Tiを含有する場合は、0.003%以上とする。より好ましくは0.005%以上、さらに好ましくは0.007%以上とする。一方、0.050%を超えて含有すると、析出物が粗大化し、母材靱性を劣化させることがある。また、粗大な炭窒化物が析出し、破壊の起点となることがある。このため、Tiを含有する場合は、0.050%以下とする。より好ましくは0.035%以下、さらに好ましくは0.032%以下とする。 Ti: 0.003 to 0.050%
Ti is an element that precipitates as a nitride or carbonitride and is effective in improving the strength of a steel sheet. In order to obtain such an effect, when Ti is contained, the content is 0.003% or more. It is more preferably 0.005% or more, still more preferably 0.007% or more. On the other hand, if it is contained in excess of 0.050%, the precipitate may become coarse and the toughness of the base metal may be deteriorated. In addition, coarse carbonitride may precipitate and serve as a starting point for fracture. Therefore, when Ti is contained, it is set to 0.050% or less. It is more preferably 0.035% or less, still more preferably 0.032% or less.
Bは、母材強度向上に有効な元素である。このような効果を得るためには、Bを含有する場合は、0.0003%以上とする。一方、0.0100%を超えて含有すると、粗大なB析出物を生成し、靭性が低下する。このため、Bを含有する場合は、0.0100%以下とする。より好ましくは、0.0030%以下とする。 B: 0.0003 to 0.0100%
B is an element effective for improving the strength of the base material. In order to obtain such an effect, when B is contained, the content is 0.0003% or more. On the other hand, if it is contained in excess of 0.0100%, a coarse B precipitate is formed and the toughness is lowered. Therefore, when B is contained, it is set to 0.0100% or less. More preferably, it is 0.0030% or less.
Cuは、焼入れ性向上により鋼板強度を高める有効な元素である。このような効果を得るためには、Cuを含有する場合は、0.01%以上とする。一方、1.00%を超えて含有すると鋼板の低温靭性が低下することに加え、鋳造後の鋼(スラブ)表面の性状が悪化するおそれがある。したがって、Cuを含有させる場合には、1.00%以下とする。より好ましくは、0.30%以下とする。 Cu: 0.01-1.00%
Cu is an effective element that enhances the strength of steel sheets by improving hardenability. In order to obtain such an effect, when Cu is contained, the content is 0.01% or more. On the other hand, if the content exceeds 1.00%, the low temperature toughness of the steel sheet is lowered, and the properties of the steel (slab) surface after casting may be deteriorated. Therefore, when Cu is contained, it is set to 1.00% or less. More preferably, it is 0.30% or less.
Snは、耐食性向上に有効な元素である。これらの元素は少量の含有でも効果を発揮するが、Snを含有させる場合は、0.01%以上とする。しかしながら、多く含有させると、溶接性や靱性を劣化させ、コストの観点からも不利になる。したがって、Snを含有する場合、0.30%以下とする。より好ましくは0.25%以下とする。 Sn: 0.01 to 0.30%
Sn is an element effective for improving corrosion resistance. These elements are effective even if they are contained in a small amount, but when Sn is contained, the content is 0.01% or more. However, if it is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, when Sn is contained, it is set to 0.30% or less. More preferably, it is 0.25% or less.
Sbは、Snと同様に、耐食性向上に有効な元素である。これらの元素は少量の含有でも効果を発揮するが、Sbを含有させる場合は、0.01%以上とする。しかしながら、多く含有させると、溶接性や靱性を劣化させ、コストの観点からも不利になる。したがって、Sbを含有する場合、0.30%以下とする。より好ましくは0.25%以下とする。 Sb: 0.01 to 0.30%
Similar to Sn, Sb is an element effective for improving corrosion resistance. These elements are effective even if they are contained in a small amount, but when Sb is contained, the content is 0.01% or more. However, if it is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, when Sb is contained, it is set to 0.30% or less. More preferably, it is 0.25% or less.
Wは、SnやSbと同様に、耐食性向上に有効な元素である。これらの元素は少量の含有でも効果を発揮するため、Wを0%超含有させることができる。しかしながら、多く含有させると、溶接性や靱性を劣化させ、コストの観点からも不利になる。したがって、Wを含有する場合、2.00%以下とする。より好ましくは0.50%以下とする。 W: Over 0 to 2.00%
Like Sn and Sb, W is an element effective for improving corrosion resistance. Since these elements are effective even when contained in a small amount, W can be contained in excess of 0%. However, if it is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, when W is contained, it is set to 2.00% or less. More preferably, it is 0.50% or less.
Coは、Sn、Sb、Wと同様に、耐食性向上に有効な元素である。これらの元素は少量の含有でも効果を発揮するため、Coを0%超含有させることができる。さらに好ましくは0.10%以上とする。しかしながら、多く含有させると、溶接性や靱性を劣化させ、コストの観点からも不利になる。したがって、Coを含有する場合、2.00%以下とする。より好ましくは1.50%以下とする。 Co: Over 0 to 2.00%
Co is an element effective for improving corrosion resistance, like Sn, Sb, and W. Since these elements are effective even when contained in a small amount, Co can be contained in excess of 0%. More preferably, it is 0.10% or more. However, if it is contained in a large amount, the weldability and toughness are deteriorated, which is disadvantageous from the viewpoint of cost. Therefore, when Co is contained, it is set to 2.00% or less. More preferably, it is 1.50% or less.
Caは、MnS等の介在物の形態制御に有効な元素であり、必要に応じて含有できる。介在物の形態制御とは、展伸した硫化物系介在物を粒状の介在物とすることをいう。この介在物の形態制御を介して、板厚中心部の板厚方向引張特性、靭性、耐硫化物応力腐食割れ性を向上させることができる。このような効果を得るためには、Caを含有する場合は0.0005%以上とする。より好ましくは0.0010%以上とする。一方、Caを多く含有させると、非金属介在物量が増加し、かえって板厚中心部の板厚方向引張特性が低下する場合がある。よってCaを含有する場合、0.0050%以下とする。より好ましくは0.0040%以下とする。 Ca: 0.0005 to 0.0050%
Ca is an element effective for controlling the morphology of inclusions such as MnS, and can be contained as needed. Morphological control of inclusions means that the expanded sulfide-based inclusions are made into granular inclusions. Through the morphological control of the inclusions, the tensile properties in the plate thickness direction, the toughness, and the sulfide stress corrosion cracking resistance of the central portion of the plate thickness can be improved. In order to obtain such an effect, when Ca is contained, the content is 0.0005% or more. More preferably, it is 0.0010% or more. On the other hand, when a large amount of Ca is contained, the amount of non-metal inclusions increases, and the tensile characteristics in the plate thickness direction at the center of the plate thickness may decrease. Therefore, when Ca is contained, it is set to 0.0050% or less. More preferably, it is 0.0040% or less.
Mgは、Caと同様に、MnS等の介在物の形態制御に有効な元素であり、必要に応じて含有できる。この介在物の形態制御を介して、板厚中心部の板厚方向引張特性、靭性、耐硫化物応力腐食割れ性を向上させることができる。このような効果を得るためには、Mgを含有する場合は0.0005%以上とする。より好ましくは0.0010%以上とする。一方、Mgを多く含有させると、非金属介在物量が増加し、かえって板厚中心部の板厚方向引張特性が低下する場合がある。よってMgを含有する場合、0.0050%以下とする。より好ましくは0.0040%以下とする。 Mg: 0.0005-0.0050%
Like Ca, Mg is an element effective for controlling the morphology of inclusions such as MnS, and can be contained as needed. Through the morphological control of the inclusions, the tensile properties in the plate thickness direction, the toughness, and the sulfide stress corrosion cracking resistance of the central portion of the plate thickness can be improved. In order to obtain such an effect, when Mg is contained, the content is 0.0005% or more. More preferably, it is 0.0010% or more. On the other hand, when a large amount of Mg is contained, the amount of non-metal inclusions increases, and the tensile characteristics in the plate thickness direction at the center of the plate thickness may decrease. Therefore, when Mg is contained, it is set to 0.0050% or less. More preferably, it is 0.0040% or less.
Zrは、CaやMg同様、MnS等の介在物の形態制御に有効な元素であり、必要に応じて含有できる。この介在物の形態制御を介して、板厚中心部における板厚方向引張特性、靭性、耐硫化物応力腐食割れ性を向上させることができる。このような効果を得るためには、Zrは0.0005%以上とする。好ましくは0.0010%以上とする。一方、Zrを多く含有させると、非金属介在物量が増加し、かえって板厚中心部における板厚方向引張特性が低下する場合がある。よってZrを含有する場合、0.0050%以下とする。より好ましくは0.0040%以下とする。 Zr: 0.0005-0.0050%
Like Ca and Mg, Zr is an element effective for controlling the morphology of inclusions such as MnS, and can be contained as needed. Through the morphological control of the inclusions, the tensile properties in the plate thickness direction, the toughness, and the sulfide stress corrosion cracking resistance at the center of the plate thickness can be improved. In order to obtain such an effect, Zr is set to 0.0005% or more. It is preferably 0.0010% or more. On the other hand, when a large amount of Zr is contained, the amount of non-metal inclusions increases, and the tensile characteristics in the plate thickness direction at the center of the plate thickness may decrease. Therefore, when Zr is contained, it is set to 0.0050% or less. More preferably, it is 0.0040% or less.
REMは、Ca、Mg、Zrと同様に、MnS等の介在物の形態制御に有効な元素であり、必要に応じて含有できる。この介在物の形態制御を介して、板厚中心部における板厚方向引張特性、靭性、耐硫化物応力腐食割れ性を向上させることができる。このような効果を得るためには、REMは0.0010%以上とする。より好ましくは0.0020%以上とする。一方、REMを多く含有させると、非金属介在物量が増加し、かえって板厚中心部における板厚方向引張特性が低下する場合がある。よってREMを含有する場合、0.0100%以下とする。 REM: 0.0010-0.0100%
Like Ca, Mg, and Zr, REM is an element effective for controlling the morphology of inclusions such as MnS, and can be contained as needed. Through the morphological control of the inclusions, the tensile properties in the plate thickness direction, the toughness, and the sulfide stress corrosion cracking resistance at the center of the plate thickness can be improved. In order to obtain such an effect, the REM is set to 0.0010% or more. More preferably, it is 0.0020% or more. On the other hand, if a large amount of REM is contained, the amount of non-metal inclusions may increase, and the tensile characteristics in the plate thickness direction at the center of the plate thickness may decrease. Therefore, when REM is contained, it should be 0.0100% or less.
鋼素材を再加熱するのは、組織中の析出物を固溶させ、結晶粒径等を均一化するためであり、加熱温度としては、1000℃以上1300℃以下とする。加熱温度が1000℃未満の場合、AlNなどの析出物が十分に固溶しないばかりか、再加熱中に粗大化して破壊の起点となるため所望の板厚方向の引張試験における絞り値が得られない。一方、加熱温度が1300℃を超えると、結晶粒径が粗大化して靭性が劣化するだけでなく、生産コストが増大する。よって再加熱温度を1300℃以下とする。好ましくは1250℃以下、より好ましくは1200℃以下とする。なお、再加熱時間は、1~10時間が好ましい。 Reheating temperature of steel material: 1000 ° C or higher and 1300 ° C or lower The reason for reheating the steel material is to dissolve the precipitates in the structure and make the crystal grain size uniform, and the heating temperature is 1000. The temperature is equal to or higher than 1300 ° C. When the heating temperature is less than 1000 ° C., not only the precipitates such as AlN do not dissolve sufficiently, but also they become coarse during reheating and become the starting point of fracture, so that the drawing value in the desired tensile test in the plate thickness direction can be obtained. Absent. On the other hand, when the heating temperature exceeds 1300 ° C., not only the crystal grain size becomes coarse and the toughness deteriorates, but also the production cost increases. Therefore, the reheating temperature is set to 1300 ° C. or lower. The temperature is preferably 1250 ° C or lower, more preferably 1200 ° C or lower. The reheating time is preferably 1 to 10 hours.
熱間圧延工程における仕上圧延の際、圧下比(スラブ厚/最終板厚)を3以上とすることにより、再結晶を促進し整粒化を図るとともに、ポロシティと呼ばれる内部微小空孔等の鋳造欠陥を圧着して無害化することができる。さらにMn、P、S等の中心偏析を低減することにより、所望の熱延板ミクロ組織として、所望の板厚方向の引張特性を得ることができる。圧下比が3未満の熱間圧延では、粗大組織が残存する、前記鋳造欠陥や中心偏析の無害化が不十分となる等、所望のミクロ組織が得られず所望の板厚方向の引張試験における絞り値が得られない。よって圧下比を3以上に限定する。好ましくは圧下比4以上、より好ましくは圧下比5以上とする。 The reduction ratio of the finish rolling is 3 or more. During the finish rolling in the hot rolling process, the reduction ratio (slab thickness / final plate thickness) is set to 3 or more to promote recrystallization and sizing, and to achieve porosity. Casting defects such as so-called internal micropores can be crimped to make them harmless. Further, by reducing the central segregation of Mn, P, S and the like, it is possible to obtain a desired tensile property in the plate thickness direction as a desired hot-rolled plate microstructure. In hot rolling with a reduction ratio of less than 3, a desired microstructure cannot be obtained due to residual coarse structure, insufficient detoxification of the casting defects and central segregation, etc., and in a tensile test in a desired plate thickness direction. I can't get the aperture value. Therefore, the reduction ratio is limited to 3 or more. The reduction ratio is preferably 4 or more, and more preferably 5 or more.
材質を最終的に決定する最終3パスのうち、少なくとも2パスについて1パス当たりの圧延形状比を0.7以上とすることで、鋳造欠陥を確実に無害化し、鋼板全体、特に板厚中心部における粗大粒の残存を抑制し整粒化することができる。その結果、板厚中心部における板厚方向引張による絞り値が向上する。ここで、圧延形状比(ld/hm)とは、{圧延ロールが鋼板と接触する長さ(ロール接触弧長:ld)}/{ロール入側の板厚と出側の板厚の平均厚さ:hm}のことをいい、(1)式で示される。
ld/hm={R(hi-ho)}1/2/{(hi+2ho)/3}
ここで、
R:各圧延パス時におけるロール半径
hi:各圧延パス時における入側板厚
h0:各圧延パス時における出側板厚
である。
圧延形状比が0.7以上のパスが2パス未満では、粗大組織が残存する、または鋳造欠陥の無害化が不十分となる等、所望のミクロ組織が得られず所望の板厚中心部における板厚方向引張による絞り値が得られない。したがって、圧延形状比が0.7以上のパスを少なくとも2パスとする。なお、圧延形状比を大きくするには、圧延ロール径を大きくする、あるいは圧下量を大きくすればよい。 Rolling shape ratio per pass for at least 2 of the final 3 passes of finish rolling 0.7 or more Rolled shape ratio per pass for at least 2 of the final 3 passes that finally determine the material By setting the value to 0.7 or more, casting defects can be reliably detoxified, and coarse grains can be suppressed from remaining in the entire steel sheet, particularly in the central portion of the sheet thickness, for sizing. As a result, the drawing value due to tension in the plate thickness direction at the center of the plate thickness is improved. Here, the rolling shape ratio (ld / h m ) is {the length of the rolled roll in contact with the steel plate (roll contact arc length: ld)} / {the average of the plate thickness on the roll entry side and the plate thickness on the exit side. thickness: refers to h m}, represented by formula (1).
ld / h m = {R ( h i -h o)} 1/2 / {(h i + 2h o) / 3}
here,
R: Roll radius at each rolling pass h i : Incoming plate thickness at each rolling pass h 0 : Outer plate thickness at each rolling pass.
If the number of passes having a rolled shape ratio of 0.7 or more is less than 2 passes, a desired microstructure cannot be obtained, such as a coarse structure remaining or insufficient detoxification of casting defects, and a desired plate thickness center portion. The drawing value due to tension in the plate thickness direction cannot be obtained. Therefore, at least two passes have a rolled shape ratio of 0.7 or more. In order to increase the rolling shape ratio, the rolling roll diameter may be increased or the rolling reduction amount may be increased.
本発明では、連続鋳造時に、スラブを軽圧下することが好ましい。本発明では、軽圧下することにより、板厚中心部における、長径が100μm以上の粗大なMnSおよび円相当径で100μm以上の粗大な旧オーステナイト粒の残存をより抑制することができる。軽圧下の条件としては、具体的に、スラブの最終凝固位置よりも上流で圧下勾配を0.1mm/m以上とすることが好ましい。 Light reduction during casting In the present invention, it is preferable to lightly reduce the slab during continuous casting. In the present invention, by lightly reducing the pressure, it is possible to further suppress the residual of coarse MnS having a major axis of 100 μm or more and coarse old austenite grains having a circular equivalent diameter of 100 μm or more in the central portion of the plate thickness. As the conditions under light reduction, specifically, it is preferable that the reduction gradient is 0.1 mm / m or more upstream of the final solidification position of the slab.
本発明では、熱間圧延後の冷却開始温度はとくに限定されず、1000℃以下500℃以上であるのが好ましい。 Cooling start temperature after hot rolling In the present invention, the cooling start temperature after hot rolling is not particularly limited, and is preferably 1000 ° C. or lower and 500 ° C. or higher.
本発明では、熱間熱延後の冷却方法はとくに限定されず、例えば、空冷、水冷など、任意の方法で行うことができる。強度、低温靭性など必要な特性を得るために、熱間圧延後、スプレー冷却、ミスト冷却、ラミナー冷却などの水冷を実施してもよい。 Cooling method after hot rolling In the present invention, the cooling method after hot hot rolling is not particularly limited, and any method such as air cooling or water cooling can be used. In order to obtain necessary properties such as strength and low temperature toughness, water cooling such as spray cooling, mist cooling, and laminar cooling may be performed after hot rolling.
本発明では、熱間圧延後冷却して最終製品とすることができるが、さらに低温靭性など必要な特性を得るために熱処理を行うことが好ましい。熱処理としては、熱間圧延後に、焼戻し処理を行うことが好ましい。また、焼戻し処理の前に焼入れ処理も行う焼入れ-焼戻し処理を行ってもよい。また、二相域焼入れ処理後に焼戻し処理を行う二相域焼入れ-焼戻し処理を行ってもよい。さらに、焼入れ-焼戻し処理の間に、二相域焼入れ処理を挟んだ、焼入れ-二相焼入れ-焼戻し処理を行ってもよい。上記いずれかのプロセスを用いて製造することが望ましい。 Heat treatment after hot rolling In the present invention, the final product can be cooled after hot rolling, but it is preferable to perform heat treatment in order to further obtain necessary properties such as low temperature toughness. As the heat treatment, it is preferable to perform a tempering treatment after hot rolling. Further, a quenching-tempering treatment may be performed in which a quenching treatment is also performed before the tempering treatment. Further, a two-phase region quenching-tempering treatment in which a tempering treatment is performed after the two-phase region quenching treatment may be performed. Further, the quenching-two-phase quenching-tempering treatment may be performed with the two-phase region quenching treatment sandwiched between the quenching-tempering treatments. It is desirable to manufacture using any of the above processes.
Ac1(℃)=750.8-26.6C+17.6Si-11.6Mn-22.9Cu-23Ni+24.1Cr+22.5Mo-39.7V-5.7Ti+232.4Nb-169.4Al…(1)
Ac3(℃)=937.2-436.5C+56Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr+38.1Mo+124.8V+136.3Ti-19.1Nb+198.4Al…(2)
ただし、上記(1)、(2)式中の元素記号は、各元素の含有量(質量%)を表し、当該元素が含有されていない場合は0とする。 The Ac 3 transformation point and the Ac 1 transformation point can be obtained by the following equations (1) and (2).
Ac 1 (° C.) = 750.8-26.6C + 17.6Si-11.6Mn-22.9Cu-23Ni + 24.1Cr + 22.5Mo-39.7V-5.7Ti + 232.4Nb-169.4Al ... (1)
Ac 3 (° C.) = 937.2-436.5C + 56Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr + 38.1Mo + 124.8V + 136.3Ti-19.1Nb + 198.4Al ... (2)
However, the element symbol in the above formulas (1) and (2) represents the content (mass%) of each element, and is set to 0 when the element is not contained.
引張特性は、厚鋼板の板厚方向が引張方向となるようにし、TypeAの形状の試験片に加工し、JIS G3199に準拠して引張試験を実施した。低温靭性は、厚鋼板の板厚方向が引張方向となるように試験片を採取した試験片を液体窒素中で-196℃に冷却し、JIS Z2242に準拠してシャルピー衝撃試験を実施し、-196℃における吸収エネルギーvE-196を求めた。
本発明では、降伏強度(YS)が585MPa以上、引張強さ(TS)が690MPa以上、破断後の絞り値(引張試験における試験前の試験片断面積Sに対する試験後の試験片断面積減少量ΔSの分率)が30%以上、vE-196が34J以上を合格とした。 (Mechanical characteristics in the plate thickness direction)
As for the tensile properties, the thickness direction of the thick steel plate was set to be the tensile direction, and the test piece was processed into a Type A-shaped test piece, and a tensile test was carried out in accordance with JIS G3199. For low temperature toughness, the test piece was collected so that the thickness direction of the thick steel plate was the tensile direction, and the test piece was cooled to -196 ° C in liquid nitrogen and subjected to a Charpy impact test in accordance with JIS Z2242. to determine the absorption energy vE -196 at 196 ℃.
In the present invention, the yield strength (YS) is 585 MPa or more, the tensile strength (TS) is 690 MPa or more, and the drawing value after fracture (the amount of decrease in the cross-sectional area of the test piece after the test with respect to the cross-sectional area S of the test piece before the test in the tensile test ΔS). fraction) of 30% or more, vE -196 was evaluated as acceptable or 34 J.
得られた鋼板から、板厚1/2位置が観察位置となるように、組織観察用の試験片を採取した。試験片を、圧延方向と垂直な断面が観察面となるよう樹脂に埋め、鏡面研磨した。次いで、ピクリン酸腐食を実施した後、倍率200倍のSEMで観察して、板厚1/2位置における組織のSEM像を撮影した。撮影した5視野分の画像を画像解析装置によって解析し、長径が100μm以上のMnSの数密度および旧オーステナイト粒の円相当径の最大値を求めた。 (Micro tissue)
From the obtained steel sheet, test pieces for microstructure observation were collected so that the plate thickness 1/2 position was the observation position. The test piece was embedded in resin so that the cross section perpendicular to the rolling direction was the observation surface, and mirror-polished. Next, after carrying out picric acid corrosion, observation was performed with an SEM at a magnification of 200 times, and an SEM image of the structure at a plate thickness of 1/2 was taken. The images of the five visual fields taken were analyzed by an image analysis device, and the number density of MnS having a major axis of 100 μm or more and the maximum value of the equivalent circle diameter of the old austenite grains were obtained.
Claims (4)
- 質量%で、C:0.01~0.15%、
Si:0.01~1.00%、
Mn:0.10~2.00%、
P:0.010%以下、
S:0.0050%以下、
Al:0.002~0.100%、
Ni:5.0~10.0%、
N:0.0010~0.0080%を含有し、残部Feおよび不可避的不純物からなる成分組成を有し、板厚中心部における板厚方向引張による絞り値が30%以上である厚鋼板。 By mass%, C: 0.01-0.15%,
Si: 0.01-1.00%,
Mn: 0.10 to 2.00%,
P: 0.010% or less,
S: 0.0050% or less,
Al: 0.002 to 0.100%,
Ni: 5.0-10.0%,
N: A thick steel sheet containing 0.0010 to 0.0080%, having a component composition consisting of the balance Fe and unavoidable impurities, and having a drawing value of 30% or more due to tension in the plate thickness direction at the center of the plate thickness. - さらに質量%で、Cr:0.01~1.50%、
Mo:0.03~1.0%、
Nb:0.001~0.030%、
V:0.01~0.10%、
Ti:0.003~0.050%、
B:0.0003~0.0100%、
Cu:0.01~1.00%から選択される1種または2種以上を含有する請求項1に記載の厚鋼板。 Further, in mass%, Cr: 0.01 to 1.50%,
Mo: 0.03 to 1.0%,
Nb: 0.001 to 0.030%,
V: 0.01 to 0.10%,
Ti: 0.003 to 0.050%,
B: 0.0003 to 0.0100%,
Cu: The thick steel sheet according to claim 1, which contains one or more selected from 0.01 to 1.00%. - さらに質量%で、Sn:0.01~0.30%、
Sb:0.01~0.30%、
W:0超~2.00%、
Co:0超~2.00%、
Ca:0.0005~0.0050%、
Mg:0.0005~0.0050%、
Zr:0.0005~0.0050%、
REM:0.0010~0.0100%から選択される1種または2種以上を含有する請求項1または2に記載の厚鋼板。 Further, in mass%, Sn: 0.01 to 0.30%,
Sb: 0.01-0.30%,
W: Over 0 to 2.00%,
Co: Over 0 to 2.00%,
Ca: 0.0005 to 0.0050%,
Mg: 0.0005-0.0050%,
Zr: 0.0005-0.0050%,
REM: The thick steel sheet according to claim 1 or 2, which contains one or more selected from 0.0010 to 0.0100%. - 請求項1~3のいずれかに記載の成分組成からなるスラブを、1000℃以上1300℃以下に加熱したのち、仕上圧延の際、圧下比3以上かつ最終3パスのうち少なくとも2パスについて、1パス当たりの圧延形状比が0.7以上とする熱間圧延を行う厚鋼板の製造方法。 After heating the slab having the component composition according to any one of claims 1 to 3 to 1000 ° C. or higher and 1300 ° C. or lower, at the time of finish rolling, the rolling reduction ratio is 3 or more and at least 2 out of the final 3 passes are 1 A method for manufacturing a thick steel sheet that is hot-rolled so that the rolling shape ratio per pass is 0.7 or more.
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